ARTICULATIONS 163 



Dissection. To display the articular surfaces of the carpo-metacarpal 

 articulations, the metacarpus should be detached from the carpus. The 

 interosseous ligaments between the carpal bones of the second row, and 

 also between the bases of the four medial metacarpal bones, can likewise be 

 demonstrated by carrying the knife between the bones, and dividing the 

 ligaments. 



Articular Surfaces. The base of the metacarpal bone of 

 the index will be seen to be hollowed out for the reception 

 of the os multangulum minus. On the lateral side it likewise 

 articulates with the os multangulum majus, and on the medial 

 side with the os capitatum. The base of the third metacarpal 

 rests against the os capitatum alone. The base of the meta- 

 carpal bone of the ring finger rests upon the os hamatum, 

 but also articulates slightly with the os capitatum. The fifth 

 metacarpal bone articulates with the os hamatum. 



Movements of the Metacarpal Bones. The opposed saddle - shaped 

 surfaces of the os multangulum majus and the metacarpal bone of the thumb 

 allow free movement at this joint. Thus the metacarpal bone of the thumb 

 can be moved (i) dorso-laterally (extension) ; (2) volarwards and medially 

 (flexion) ; (3) medially towards the index (adduction) ; (4) laterally (abduc- 

 tion) ; (5) medially across the palm towards the little finger (opposition) ; 

 (6) a combination of the above-mentioned movements occurring one after 

 the other constitutes circumduction. The muscles which operate on the 

 thumb are (i) the two special extensors, brevis and longus, and the 

 abductor pollicis longus producing extension ; (2) the flexor pollicis brevis, 

 the opponens pollicis, and the adductor pollicis producing flexion and 

 opposition, two movements which are similar in character ; (3) the 

 abductor pollicis longus and the abductor pollicis brevis producing 

 abduction ; (4) the adductor pollicis and the first dorsal interosseous 

 muscle which give rise to adduction. 



The metacarpal bones of the index and middle fingers possess very 

 little power of independent movement. The metacarpal bone of the ring 

 finger, and more especially the metacarpal bone of the little finger, are 

 not so tightly bound to the carpus. When the hand is clenched they both 

 move volarwards. The metacarpal bone of the little finger is provided 

 with an opponens muscle, and has a feeble power of moving volarwards 

 and laterally towards the thumb. 



ARTICULATIONES METACARPOPHALANGE^E (METACARPO- 

 PHALANGEAL JOINTS). 



The slightly cupped base of the first phalanx of each 

 digit articulates with the rounded head of the corresponding 

 metacarpal bone, and is held in position by (i) a capsule; 

 (2) two ligg. collateralia, and (3) by a lig. accessorium volare. 



Lig. Accessorium Volare (O.T. Anterior Ligament). The 

 volar accessory ligament is a dense fibrous plate placed on the 

 volar aspect of the joint. It is firmly attached to the base 



i 11 a 



